1. Field of the Invention
The present invention relates to an input buffer circuit and a semiconductor apparatus having such input buffer circuit.
2. Description of Related Art
Conventionally, input buffer circuits are installed at input sides of various circuits in order to input signals having predetermined levels to various circuits built or formed in a semiconductor apparatus. This input buffer circuit is designed so as to be operated at a power source voltage used inside the semiconductor apparatus.
However, in association with smaller size and lower electric power consumption of the semiconductor apparatus in recent years, the power source voltage used inside the semiconductor apparatus is lowered. On the other hand, among other devices mounted on the same substrate of the semiconductor apparatus, such devices that are operated at a voltage higher than the power source voltage used inside the semiconductor apparatus still exist.
For this reason, the conventional semiconductor apparatus was designed such that the input buffer circuit was divided into an input side circuit and an output side circuit, wherein the input side circuit was driven by an external power source voltage used outside the semiconductor apparatus, and the matching with the other device was consequently attained. On the contrary, the output side circuit was driven by an internal power source voltage used inside the semiconductor apparatus, and an electric power consumption was consequently reduced. Moreover, the conventional semiconductor apparatus was designed such that since a drive voltage was different between the input side circuit and output side circuit of the input buffer circuit, a threshold of an output potential on the input side circuit and a threshold of an input potential of the output side circuit were different to each other, and for this reason, a signal level converting circuit for shifting a level of a signal had to be installed between the input side circuit and the output side circuit. That is, this signal level converting circuit was used to try to match the threshold of the output potential of the input side circuit and the threshold of the input potential of the output side circuit. One of the conventional input buffer circuits is disclosed in Patent Document 1: Japanese Laid Open Patent Application No. JP-A-Heisei 6-21800.
However, the above-mentioned conventional input buffer circuit was designed so as to use the signal level converting circuit installed between the input side circuit and the output side circuit, and to match the threshold of the output potential of the input side circuit and the threshold of the input potential of the output side circuit. Thus, if any variation was induced in the external power source voltage used outside the semiconductor apparatus, the threshold of the output potential of the input side circuit was also varied. Hence, even if the signal level after the variation was converted by the signal level converting circuit, it could not be made coincident with the threshold of the input potential of the output side circuit.
For this reason, in the conventional input buffer circuit, if the variation was induced in the external power source voltage used outside the semiconductor apparatus, the threshold of the output potential of the input side circuit and the threshold of the input potential of the output side circuit was not matched, and there was a fear that the output side circuit was erroneously operated. This fact consequently brought about a fear that the various circuits at later stages connected to the input buffer circuit could not be normally operated.